Green hydrogen, what is it?

Green hydrogen is making headlines and emerging as the latest major trend in the energy revolution, but do we know what it is, what it is used for, and how it is produced?

 

 

We are facing a real technological challenge to curb the impact of human activity on the planet. Our dizzying economic and social development—through industrial revolutions—has gone hand in hand with a dangerous increase in our carbon footprint, jeopardizing the climate balance and, therefore, the ecosystems and life on our planet. A reality of which, fortunately, we are increasingly aware every day—perhaps not sufficiently—and which, as a society, we want to curb through different solutions that allow us to stop polluting and damaging our planet, while ensuring an improvement in the quality of life for all people. Thus, in recent decades, investment in innovation and technology has allowed us to develop different solutions for generating green energy, reducing pollution, and eliminating and/or replacing emissions of harmful components into the atmosphere with more harmless ones. In short, human beings are trying, although not yet with the necessary global consensus, to curb a very important problem for both humanity itself and the planet. With this, over the last ten years we have been experiencing revolutionary changes in sectors such as transportation, in which two protagonists have been (re)born: the electric vehicle (it should be remembered that the first vehicles had electric motors and not combustion engines) and the hydrogen vehicle. It is precisely on this last point that we want to focus. And the thing is, do we know what hydrogen is or, even more complex, green hydrogen and how it can change the transportation sector or at least a fundamental part of it? Let’s go for it.

As we explained, every activity leaves a mark; something that is evident in our current mobility model based on the combustion of fossil fuels. Whether diesel, gasoline, or kerosene (mainly used in aviation), fossil-based combustion engines obtain mechanical energy through the chemical energy of a fuel burning in a combustion chamber. This means that huge amounts of polluting gases and particles such as nitrous oxides, carbon monoxides, carbon dioxide, as well as other volatile organic compounds and particulate matter of various types end up entering our atmosphere, causing more than evident damage to our health and the environment. For this reason, for years there has been an effort to find alternatives to these fossil fuels for use in our vehicles. A search that in recent decades has resulted in us being able to classify these alternative technologies into two large groups, with significant differences depending on the trends in the sector that we can observe today, and which cannot be analyzed on the same level, but rather according to their particularities and possible uses in a close scenario. Thus, we proceed to distinguish between these two coexisting technologies:

 

• Electric motors: Their operation is based on one or more electric motors that, powered by batteries, generate resistance and convert kinetic energy (movement) into alternating current, which passes again through the converter to become direct current and, in turn, is stored again in the battery to be used again. It seems that this solution is the one that is establishing itself as the alternative to combustion engines for passenger cars and daily commutes; although it is still too early to know what its representation will be in the vehicle market. What is clear is that it is a key solution for decarbonizing transport if it is supported by the use of renewable energies.

 

• Hydrogen combustion engine: It works with a fuel cell, which we find in the front of the vehicle, and which, through a chemical reaction with the oxygen obtained from outside the vehicle, produces electricity to move the car. The surplus produced by this process is only water vapor. Another thing is how said hydrogen is produced and how much we pollute in said production process, hence the importance of the type of hydrogen used. This solution seems ideal for those transport methods that require high autonomy and power, as well as in gas-intensive industrial processes. This is where the famous green hydrogen comes in again; now we will see why.

 

Green hydrogen, and other types of hydrogen to complete a rainbow 

As we said, the production and/or obtaining of hydrogen is so important in this process that it totally determines the carbon footprint we generate with the use of each technology. First of all, it must be explained that hydrogen is not a compound that can be captured freely in our natural environment, it is present but not in the quantity or form necessary for its capture, but rather it is what in chemistry is called an “energy vector”, and is also light and easily storable. This basically means that its production requires a process subject to the use of energy; that is, depending on the energy source we use, hydrogen can generate a carbon footprint of different kinds. Well, the greener the hydrogen production process is, the greener the hydrogen itself will be.

Perhaps, knowing this, the most important thing is to know the differences between the different types of hydrogen that exist depending on the way in which it is produced. Thus, we can speak, as if it were a martial arts belt, of eight color classifications, despite the fact that hydrogen itself has no color as such, with the following differences:

 

Black/brown hydrogen

It is the one produced as a result of the gasification of carbon through the burning of different carbon minerals such as bituminous coal (black), or hard coal and lignite (brown). Since it is based on pure combustion, various polluting emissions, including carbon dioxide, are released into the atmosphere as part of the chemical process. This is why it is considered the most harmful type of hydrogen for the environment.

Gray hydrogen

This is the most common and easiest color of hydrogen to produce (therefore the cheapest), although it is also one of those that releases the greatest amount of carbon dioxide into the atmosphere. Grey hydrogen is produced through what is known as steam reforming (SMR) of fossil fuels, especially natural gas.

Yellow hydrogen

Yellow hydrogen is hydrogen in which the electricity used for electrolysis comes from a variety of generation sources, including both those based on renewable energy and those that use fossil fuels. The peculiarity is that yellow hydrogen also refers to hydrogen produced using solar energy, although this would be classified as a whole within green; in fact, we could argue that it is a shade of green hydrogen.

Blue hydrogen

Turquoise Hydrogen

It is obtained through a revolutionary method, disclosed by the Japanese industrial company Ebara, which allows the extraction of methane contained within natural gas and biogas through methane pyrolysis. As a result, the carbon produced in the process ends up in a solid state and is not released into the atmosphere, making its recapture and storage unnecessary and can be used in the manufacture of a series of other useful carbon-based products, such as fertilizers.

Despite everything, this process is still in the development phase; so it cannot be evaluated or produced at the same level as the other colors of hydrogen.

Pink hydrogen

This is a type of hydrogen that appears through the electrolysis of water, breaking down the water molecule to obtain hydrogen and oxygen, with a great peculiarity: the electrical energy used in the process is nuclear. It is an almost sustainable hydrogen, given that its environmental footprint is only related to nuclear energy itself.

Green hydrogen

This type of hydrogen is our great protagonist today. It is produced through the electrolysis method, breaking down the water molecule to obtain hydrogen and oxygen with a peculiarity: it only uses electrical current from renewable sources. That is to say, green hydrogen is the only one obtained with 100% clean energy such as photovoltaic (yellow), wind or hydroelectric and does not produce any direct emissions of carbon dioxide into our atmosphere.

White hydrogen

When we talk about white hydrogen, we are talking about that which is found naturally free, normally in gaseous form in the atmosphere and, sometimes, in underground deposits. The big problem is that this type of hydrogen does not have a technological strategy that allows us to use it on a large scale, so it is useless for our purpose.

How is green hydrogen produced?

As we have seen, there are a multitude of processes that result in hydrogen, although not all of them can be considered sustainable as such. This is why, in order to clarify how H2 is produced, we are going to focus on trying to unravel how the main protagonist of this article is manufactured: green hydrogen.

Let’s see, hydrogen is still a chemical element of the periodic table – specifically the first on the list – which, in this case, is obtained through the separation of the molecules that form water (H2O) through a process of dissociation of said molecules by the contribution of electricity. This process, called electrolysis, allows the separation of hydrogen molecules from oxygen molecules, and in the case of green hydrogen, it is done thanks to the electrical energy generated by any renewable energy source (mainly wind and/or photovoltaic energy).

 

In this way, the electric current is applied continuously within said electrolyzer, a process for which we must previously convert said alternating current to direct current thanks to power electronics and devices called rectifiers. For these rectifiers to operate at the appropriate levels of alternating current and voltage coming from the grid, they must be protected against possible alterations; therefore, we use transformation centers, equipped with grid protection cells, as well as transformers to adjust the levels. Something that makes them key elements for correct operation and that requires a high technological and innovative level. However, this process presents two dilemmas:

1. In the event that the electrolysis process is carried out by connection to the electrical distribution grid, the coupling will be carried out by means of connection and sectioning centres to the public distribution networks.
2. In the event that the electrolysis process starts from the electrical transmission networks, we require electrical substations; since we must transform the electricity from high to medium voltage; guaranteeing the safety of the process at all times and its correct operation.

In any case, the basic scheme would be that of an X quantity of water stored and/or transported to a hydrogen generation plant that passes through an electrolyzer to be subjected to a molecular separation process, using electrical energy of renewable origin, which breaks down its initial molecular composition. It is after this separation that the oxygen is stored for industrial or medical use and/or expelled from the equation via the atmosphere, while the hydrogen is sent to storage tanks, where it is kept as a compressed gas, or liquefied for use in industries or hydrogen fuel cells.

This is the journey that allows a simple drop of water to be converted, thanks to renewable energy and electrical infrastructure, into a green fuel with zero emissions. This is why the development of this industry is so important.